Annual influenza vaccination of the U.S. elderly population has been
demonstrated as safe and effective in reducing the risks of illness, hospitalization,
and death.1 The Medicare Current Beneficiary Survey (MCBS) has
measured annual influenza vaccination rates since 1991; the latest data available
are for the 2001-02 influenza season. Since 1996, self-reported reasons for
not receiving influenza vaccine also have been measured. During 1991-2002,
MCBS indicated a steady upward trend in vaccination coverage among Medicare
beneficiaries, with the exception of the 2000-01 influenza season, when vaccine
distribution was delayed. The most frequently cited reasons for not receiving
influenza vaccine were (1) not knowing that influenza vaccination was needed
and (2) concerns that vaccination might cause influenza or side effects. During
the 2000-01 influenza season, vaccine shortage or unavailability was noted
for the first time as an important reason for nonvaccination. Further efforts
are needed to educate the elderly regarding the benefits of influenza vaccination
and to address any concerns regarding the safety of the vaccine.

MCBS is a nationally representative survey of the Medicare population,
conducted by the Centers for Medicare & Medicaid Services (CMS). Beneficiaries
sampled from Medicare enrollment files (or appropriate proxies) are interviewed
in person. Primary sampling units (PSUs) consist of persons in 107 geographic
areas chosen to represent the nation; beneficiaries residing in these PSUs
are selected by systematic random sampling within age strata. Data for this
report were analyzed by using statistical software to account for sampling
weights in calculating point estimates of proportions; analyses were restricted
to Medicare beneficiaries aged ≥65 years who resided in a noninstitutional
setting.

Each year, MCBS asks respondents, “Did you have a flu shot for
last winter?” The percentage reporting receipt of influenza vaccination
increased each influenza season from 1991-92 through 1999-2000, and especially
in 1993-94, when influenza vaccination first became a Medicare benefit. However,
during the 2000-01 influenza season, the vaccination rate declined instead
of maintaining an annual increase; 67.0% (20.5 million of 30.6 million Medicare
beneficiaries aged ≥65 years living in the community) reported receiving
the vaccine, compared with a record high of 70.0% (21.2 million out of 30.3
million) in 1999-00. For the 2001-02 influenza season, 68.8% (21.3 million
of 31.0 million) reported receiving influenza vaccine.

The MCBS also asks about reasons for not getting influenza vaccination.
The question asked is “Why didn’t you get a flu shot for last
winter?” Respondents are free to give any reason or reasons, with open-ended
responses recorded by interviewers into prespecified categories. This question
was omitted for the 1999-00 influenza season.

The leading reasons for nonvaccination reported for 1997-98, 1998-99,
2000-01, and 2001-02 were not knowing that influenza vaccination was needed
and concerns that vaccination might cause influenza or side effects. In 2000-01,
for the first time, one of the leading reasons was that vaccine was unavailable
or in short supply. For the 2000-01 season, 12.7% of unvaccinated respondents
reported vaccine unavailability as a reason for not receiving influenza vaccine.
This equates to approximately 1.25 million persons, or 4.2% of the total elderly
Medicare population living in the community, which amounts to roughly the
difference between the expected annual increase and the actual decline for
2000-01 in self-reported influenza vaccination. By contrast, during the 2001-02
influenza season, an estimated 7.5% of unvaccinated respondents (approximately
707,000 persons, or 2.3% of the total elderly Medicare population living in
the community) reported vaccine unavailability as a reason for nonvaccination.

For the 2000-01 influenza season, production delays created shortages
of influenza vaccine, especially at the beginning of the vaccination period
(i.e., October and November), when demand was greatest.2 Delays
in vaccine production continued for the 2001-02 influenza season but were
considered less severe.3 The 2000-01 decline and subsequent rebound
of vaccination coverage in 2001-02 was observed by other government health
surveys.4,5,6 However, the self-reported MCBS data establish an
association between vaccine shortages and reduced vaccination rates among
the Medicare population aged ≥65 years, one of the groups at high risk
for influenza complications.

The findings in this report are subject to at least two limitations.
First, vaccination status during the preceding influenza season is self-reported
and subject to recall and social desirability bias. Second, the results are
subject to survivor bias (i.e., persons who died could not be interviewed
about their vaccination status the previous winter). Finally, participant
reasons for nonvaccination are categorized during the interview, rather than
recorded verbatim. Although “other” reasons are captured as a
category and reviewed for retrospective categorizing of responses, interviewer
coding might result in misclassification or in a different distribution of
reasons than would be obtained by providing respondents a list of answers
from which to choose.

Consequences from the vaccine shortage in 2000-01 were limited because
of the mildness of the influenza virus that season.7 CDC has previously
estimated that for each 1 million elderly persons vaccinated, approximately
900 deaths and 1,300 hospitalizations are prevented.8 Influenza
vaccination rates are used as indicators of progress toward achieving the
national health objectives for 2010. CMS, together with CDC, has conducted
a long-term, structured campaign to promote the benefits of vaccination to
Medicare beneficiaries and to improve provider performance. These efforts
have resulted in large increases in vaccination during the preceding decade.
However, even the strongest efforts of government agencies to promote vaccination
are subject to the constraints of limited vaccine supply. During the current
influenza vaccine shortage, vaccine is prioritized for populations at high
risk, including the elderly.

During 1997-2002, other reasons for nonvaccination were cited more often
than reduced availability of vaccine. The most common reasons for nonvaccination
were lack of knowledge about the need for vaccination and misconceptions about
influenza vaccination and disease or side effects.9 These reasons
remain important modifiers of elderly Medicare beneficiaries’ behavior
and can be further addressed through communications about influenza vaccination.
Evidence-based strategies should be developed and used to (1) educate the
public and vaccination providers regarding the benefit of influenza vaccine
for the elderly and (2) address concerns about the safety and efficacy of
the vaccine.